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P.A.S. Rack and SVA
romer - 18/1/06 at 11:33 AM

Well, following on from my earlier thread re PASvManual racks.

I've just been to see the local friendly SVA man and he said that he couldn't see any issues with using a PAS rack with threaded bungs screwed into where the PAS pipes would have normally fitted.

Some of you commented that they thought they would fail SVA.

Has anyone actually tried this and failed - ie talking from experience?

Going by our SVA guy I'm going to go PAS rack - for the quicker ratio - not to mention the donor I've got has one in !

Comments ??

Regards,

Romer

britishtrident - 18/1/06 at 12:03 PM

quote:
Originally posted by romer
Well, following on from my earlier thread re PASvManual racks.

I've just been to see the local friendly SVA man and he said that he couldn't see any issues with using a PAS rack with threaded bungs screwed into where the PAS pipes would have normally fitted.

Some of you commented that they thought they would fail SVA.

Has anyone actually tried this and failed - ie talking from experience?

Going by our SVA guy I'm going to go PAS rack - for the quicker ratio - not to mention the donor I've got has one in !

Comments ??

Regards,

Romer


This was very a big issue with MOTs about 4 years back -- istr the powers that be issued guide lines on it.

With brake servos or PAS it is deemed insufficient just to disconnect the disconnect the pipes. The Servo or power steering equipment must be completely removed and the vehicle equiped with non powered items.

Your SVA man clearly dosen't his job -- power racks have built in lost motion to operate the hydraulic valve, this isn't significant when the rack operates in powered mode but operating in the long term without power assistance it will fail. Also note if you put threaded bungs i the holes a hydraulic lock will result you won't be able to turn the steering.

James - 18/1/06 at 12:09 PM

Romer,
What happens with the fluid system in a PAS rack when you chop out the middle of the rack to fit it in your car?

Cheers,
James

smart51 - 18/1/06 at 12:10 PM

quote:
Originally posted by britishtrident
...if you put threaded bungs i the holes a hydraulic lock will result you won't be able to turn the steering.


Not if you drain the PAS fluid surely?

A PAS rack has a ring cast onto it that seals against the housing. The pressure of the fluid pushes against this, creating the assistnce force. If you turned off this ring and sealed up the fluid holes then wouldn't you be back to a manual rack?

Bluemoon - 18/1/06 at 12:25 PM

As well as the built in lost motion, I don't think the mechanics of PAS are as robust as a none PAS, as they are desgined to take less force on the rack and pinion..

romer - 18/1/06 at 12:58 PM

Yeah, this one's obviously not as cut and dryed as I thought it would be.

I was forgeting that the rack housing would have to be chopped to fit into the chassis.

Need to look into this - I'm looking to strip the rack and a normal one to see what's what. Will report back with any findings.

Anyone else for comments?

Romer

locost_bryan - 18/1/06 at 11:36 PM

quote:
Originally posted by smart51
Not if you drain the PAS fluid surely?


The PAS fluid is also the lubricant

I had a cam belt break in an auto approaching a bend - the ECU shut off the engine and it was REALLY hard to turn the wheel - the power assistance became power resistance

It seems to make sense that if the idea of PAS is to reduce the force you need to apply to the wheel, then it will also reduce the load applied to the pinion - so the pinion may not be designed to take the load when not assisted.

NS Dev - 19/1/06 at 10:35 AM

quote:
Originally posted by romer
Yeah, this one's obviously not as cut and dryed as I thought it would be.

I was forgeting that the rack housing would have to be chopped to fit into the chassis.

Need to look into this - I'm looking to strip the rack and a normal one to see what's what. Will report back with any findings.

Anyone else for comments?

Romer


I have already stripped down a sierra power racxk and non-power rack.

As I have said numerous times on here, and BritishTrident has now also pointed out, the pinion shaft is in two pieces with a flexible link which operates the valve as it moves. Running this without assist is dubious.

I looked at doing it on my Pug 205 RWD with a sierra rack, but then decided that for the sake of saving £50 over a quickrack it wasn't worth doing, especially taking the breakage risk into account.